1. Field of the Invention
The present invention relates to an optical disc device for recording and/or reproducing information by using laser beams, which is particularly suitable for adjusting a set value of laser power.
2. Description of the Related Art
Recently, various optical recording media such as a compact disc (CD) and a digital versatile disc (DVD) have been commercialized and are widely available. With respect to the optical recording media, in general, laser power is optimized on a system side before recording/reproducing operations because optimum laser power is changed according to a medium.
For example, laser power setting processing using a β value is performed for a CD-R and a DVD-R. That is, test data is recorded with predetermined laser power on a trial write area formatted on the medium. A β value is obtained from an amplitude value of a reproduced RF signal (asymmetry) of the test data. Recording Laser power is set such that the obtained β value becomes a target β value required for the medium (disc).
For example, a method described in JP 2002-260230 A has been known as a method of setting recording laser power using the β value.
When a system state (medium temperature etc.) changes after the setting of the recording laser power as described above, for example, the recording sensitivity of the medium is changed from an initial state. With this change, the recording laser power initially set is gradually deviated from an adequate value. In order to solve such a problem, on the system side, the initially set recording laser power is generally adjusted as appropriate according to a current system state.
For example, in a system for performing recording/reproducing on the CD-R and the DVD-R, a reflection light intensity caused by the initially set recording laser power is held as an amplitude level of a photo detector. An amplitude level obtained during recording operation is compared with the amplitude level in the case of the initially set recording laser power. A set value of the recording laser power is dynamically changed so that both amplitude levels become equal to each other.
However, in this case, it is necessary to perform processing for adjusting the laser power in parallel with the recording operation. Therefore, a processing sequence performed during the recording operation, which has been regarded as complicated up to now, is further complicated, so such a problem that a processing load to a microcomputer further increases occurs.
In recordable media using as a material for a recording layer an organic dye material, for example, a CD-R and a DVD-R, the sensitivity of the recording layer depends on a wavelength of laser light. Therefore, when a wavelength of laser light emitted from a semiconductor laser is varied with a change in temperature of the semiconductor laser, a phenomenon in which a recording state is changed according to the wavelength even in the case of the same intensity occurs. Thus, as described above, when the amplitude level of the reflection light is monitored to adjust the laser power, there occurs such a problem that the laser power cannot be adequately adjusted.